Method and device for welding structural parts

ABSTRACT

A method and device are provided for welding structural parts, preferably of a gas turbine, especially of an aircraft engine. A structural component is laser-welded by means of at least one laser source, the one or more laser sources being operated in a pulsed mode. Pulse duration and/or pulse shape and/or output of the one or more laser sources are adjusted in a variable manner. The wire advance of the welding wire is controlled subject to the pulses of the one or more laser sources.

The present invention relates to a method for welding structuralcomponents, preferably of a gas turbine, in particular of an aircraftengine, according to the definition of the species in claim 1. Thepresent invention also relates to a device for welding structuralcomponents, preferably of a gas turbine, in particular of an aircraftengine, according to the definition of the species in claim 11.

Gas turbines, in particular aircraft engines, must meet exceedinglystringent requirements in terms of reliability, weight, performance,economy and service life. In recent decades, aircraft engines have beendeveloped, particularly for use in the civil sector, which have fullysatisfied the above requirements and have attained a high level oftechnical perfection. The selection of material, the search for newtypes of suitable material, as well as the quest for novel manufacturingprocesses have played a decisive role in aircraft engine development.Since gas turbines are subject to high stresses and, therefore,defective regions may form on the gas turbine during operation, it isalso crucial that highly developed repair processes be devised, toenable the defective regions to be repaired reliably, safely, quicklyand cost-effectively.

The most important materials employed today for aircraft engines orother types of gas turbines are titanium alloys, nickel alloys (alsocalled superalloys) and high-strength steels. The high-strength steelsare used for shaft parts, gear parts, for the compressor housing and theturbine housing. Titanium alloys are typical materials used forcompressor parts, in particular for compressor blades. Nickel alloys aresuited for the heat-exposed parts of the aircraft engine, thus, forexample, for the turbine blades. The latest generation of gas turbinecomponents is manfactured from directionally solidified ormonocrystalline materials, besides being weight-optimized, thecomponents also being structurally designed to have ever thinner wallthicknesses.

The tendencies described above in the development of gas turbinecomponents, namely the search for increasingly improved materials, andthe increasingly weight-optimized structural components, place very highdemands on the manufacturing processes, as well as on the repairprocesses, which also include welding processes.

The present invention relates to a novel welding method, in particularrepair welding method, for structural components, in particular for gasturbine components. Thus, highly heat-resistant superalloys, which,namely, may be present as directionally solidified materials and asmonocrystalline materials, exhibit a high susceptibility to cracking andto distortion during welding processes. Accordingly, structuralcomponents made of the above materials are only workable or repairableto a less than satisfactory extent using conventional welding methods.

The German Patent No. DE 43 27 189 C2 describes a repair welding methodfor the blades of gas turbines. The method it discusses provides for abutt welding of a previously prepared repair surface, either plasma arcwelding (PAW), laser-beam welding or electron beam welding being used asthe butt welding method. In this case, a CO₂ laser is used as a lasersource.

The German Patent No. DE 196 30 703 C2 describes a method and a devicefor the repair welding of structural components manufactured from anickel-based alloy. In the repair welding method according to GermanPatent No. DE 196 30 703 C2, the structural component to be welded isinductively heated, either tungsten-inert-gas welding (TIG) or plasmaarc welding being used as the welding method.

The disadvantage associated with all of the related art welding methods,in particular repair welding methods, is that relatively high levels ofheat are introduced into the structural component to be welded duringthe welding process. It holds especially for thin-walled components madeof superalloys, in particular for directionally solidified ormonocrystalline materials, that the high levels of heat introduced intothe structural component can lead to a penetration defect, localizedcollapsing of the molten weld pool, distortion on the structuralcomponent, or to new or expanded crack formations. Excessive weldsagging can arise when working with double-walled components.Accordingly, the welding methods known from the related art requiresubstantial outlay for postprocessing. Moreover, there are considerablefluctuations in the quality obtained using the welding methods accordingto the related art.

Against this background, the object of the present invention is todevise a novel method, as well as a novel device for welding structuralcomponents, preferably of a gas turbine.

This objective is achieved in that the method mentioned at the outset isfurther refined by the features set forth in the characterizing portionof claim 1.

In accordance with the present invention, the or each laser source isoperated in pulsed mode. In the welding method according to the presentinvention, heat is introduced into the structural component to be weldedselectively and at very minimal levels. The energy introduced into thestructural component to be welded and thus the heat input introduced areprecisely controllable. The method according to the present inventionmakes it possible to produce very thin and reproducible weld seams, evenwhen working with structural components made of superalloys, inparticular of directionally solidified or monocrystalline materials, andwhen welding thin-walled components. The welding quality is improved andany reworking necessitated by recurring cracks, penetration defects,component distortion and the like is reduced to a minimum. The weldingmethod according to the present invention may be effectively implementedwithout preheating the structural components to be welded.

One advantageous aspect of the present invention provides for a weldingwire to be automatically advanced into the area of the laser beam of theor of each laser source, a control device determining a wire feed rateof the welding wire as a function of the pulse duration and/or pulseshape and/or power output of the or of each laser source and,respectively, of the corresponding laser beam.

The laser welding of the structural component is preferably carried outin an unpreheated state of the structural component under an inert gasatmosphere.

The device according to the present invention is defined in independentclaim 11 and is preferably constituted as a handheld laser device. Themethod according to the present invention, as well as the deviceaccording to the present invention are preferably used for weldingstructural components made of a directionally solidified or of amonocrystallinematerial.

Preferred embodiments of the present invention are derived from thedependent claims and from the following description.

The present invention is described in greater detail in the following onthe basis of exemplary embodiments, without being limited thereto.Reference is made to the drawing, whose:

FIG. 1 shows a schematized representation of a device according to thepresent invention for implementing the method according to the presentinvention.

The method and the device according to the present invention for thewelding, in particular the repair welding of structural components,preferably of a gas turbine, are clarified in greater detail in thefollowing. FIG. 1 shows one preferred exemplary embodiment of a deviceaccording to the present invention for welding gas turbine components,the device being designed as a handheld laser device.

In the exemplary embodiment of FIG. 1, a structural component 10 to bewelded is placed in a welding receptacle or holding receptacle 11. Inthe illustrated exemplary embodiment, structural component 10 is in theform of a gas turbine blade.

Laser welding is used to weld structural component 10 in holdingreceptacle 11. The device according to FIG. 1 includes a laser source12, the laser light produced by laser source 12 being conducted via anoptical fiber 13 into the area of a processing station 14. Processingstation 14 includes optical elements 15, 16 in order to focus the laserlight produced by laser source 12 and to deliver it as a preciselydirected and aimed laser beam 17 to structural component 10 to bewelded. The welding process may be monitored or observed using astereomicroscope 18 assigned to processing station 14.

Along the lines of the present invention, laser source 12 is operated inthe so-called pulsed mode. Accordingly, the laser welding is carried outin a pulsed mode, a pulsating laser beam 17 being used to weld thestructural component. In this connection, the pulse duration and/orpulse shape and/or power of laser beam 17 or of laser source 12 arevariably settable. Welding may be carried out both in continuous-pulseoperation as well as in single-pulse operation. The pulse shape, pulseduration, and the power of laser beam 17 are preferably controlled by acontrol device (not shown). This permits a very selective directing orfocusing of laser beam 17 at structural component 17, with the resultthat the energy introduced by laser beam 17 is precisely controllable.The heat input during the welding process using the pulsed method isvery low, obviating the need for an oversized molten weld pool. Byemploying the pulsed laser welding method, any deformation, partsdistortion, microstructural changes and cracking on structural component10 to be welded are reduced to a minimum.

The pulsed-operation laser welding method according to the presentinvention may be applied very advantageously to thin-walled componentsmade of superalloys existing in directionally solidified ormonocrystalline form. These structural components are, in particular,gas turbine blades. Structural components of this kind are particularlysensitive during welding processes and, by employing the methodaccording to the present invention, are able to be welded without beingpreheated, i.e., in the unpreheated state. As a result, gas turbineblades are able to be repaired very reliably, safely, quickly andcost-effectively. The pulsed laser welding method according to thepresent invention makes it possible for worn edges of gas turbine bladesto be rewelded while achieving exceptionally high contour accuracy, andfor cracks in the turbine blades to be reliably closed.

The device according to the present invention also includes a wirefeeder 19. Wire feeder 19 advances a welding wire 20 into contact withstructural component 10 to be welded. In accordance with the presentinvention, wire feeder 19 is controlled by the control device (notshown) in such a way that a wire feed rate of welding wire 20 is adaptedto the pulse duration and/or pulse shape and/or power output of thepulsed laser welding method. The wire feed rate is controlled in such away that welding wire 20 is precisely fed per welding pulse, intocontact with structural component 10 to be welded. In the process, thewire feed rate is preferably set as a function of the laser power. Usingempirically ascertained welding parameters, which are stored in adatabase of the control device (not shown), the requisite weldingparameters may be retrieved as a function of the particular damage. Toenhance process reliability, the present invention provides for a CNCmachine that is driven by the control device (not shown) to be used forfeeding welding wire 20.

Structural component 10 to be repaired is welded in holding receptacle11, preferably shielded by an inert gas atmosphere. An inert gas isintroduced via an inert gas feed line 21 into holding receptacle 11. Asuitable inert gas is selected by one skilled in the art whom thistechnical teaching concerns, in dependence upon the materials of thestructural components to be welded.

A solid state laser, preferably an Nd-YAG solid state laser, is used aslaser source 12. This solid state laser is operated in pulsed mode andis controllable by a control device. A pulsed solid state laser ispreferably used, whose average laser power output is within the rangefrom 100 W to 500 W, the peak pulse power being between at least 6 to 10kW. The pulse power fluctuates between 0.1 to 80 J, and the pulseduration is variably settable between 0.1 and 30 ms. The solid-statelaser is optically excited; it is preferably designed as a diode-pumpedor lamp-pumped solid-state laser.

The device according to the present invention as illustrated in FIG. 1is designed as a stationary handheld welder and, accordingly, as ahandheld laser unit. Thus, in the described preferred exemplaryembodiment, in which a control device controls the pulse duration, pulseshape and power of laser beam 17, as well as the wire feed for weldingwire 20, an operator merely needs to guide structural component 10 to bewelded, underneath laser beam 17, and observe the quality of the weldingoperation through stereomicroscope 18. In rigid or linear applications,a triaxial system may optionally be used for feeding the structuralcomponent. Besides a motor driven, controlled wire feed for welding wire20, it is self-evident that a manual wire feed operation is possible aswell. However, the motor driven, controlled wire feed is more preciseand thus preferred.

The above described specific embodiment of the device according to thepresent invention as a stationary handheld welder is primarily suitedfor processing, namely for welding or repair welding relatively smallgas turbine components, such as gas turbine blades. To process largerstructural components or to perform welding operations directly on thegas turbine, the device according to the present invention may also berealized as a mobile welding device. A specific embodiment of this kindmakes it possible for large-volume, heavy, and hard-to-reach structuralcomponents to be processed as well. In such a case, processing station14 is mounted on an articulated arm that is movable into the area of thestructural component to be welded. It is also conceivable for processingstation 14 to be advanced by a multiaxis gantry-type system to thestructural component to be processed. In this case, the device accordingto the present invention is designed as a gantry-type system.

The method according to the present invention, as well as the deviceaccording to the present invention are preferably used for the welding,in particular repair welding of structural components ofhigh-temperature-resistant superalloys having a directionally solidifiedor monocrystalline form. By employing the novel method, structuralcomponents of gas turbines, such as axially symmetrical components, forexample seals and retaining rings, may be welded. In addition to housingparts, rotor blades, as well as guide vanes of high-pressure turbines,low-pressure turbines and compressors may be welded. All superalloyγ′-phase materials, materials from the MCrAlY family, and allhigh-temperature alloys, as well as alloys from the nickel group orcobalt group are able to be reliably welded. Examples of materials thatare weldable using the method according to the present invention,include: R′80, R′41, DSR′142, R′N5, R′N4, PWA 1426, PWA 1484, PWA 1480,MARM 509 or also MARM 274. As a welding wire, primarily one is usedhaving the same composition as the structural component to be welded.

By employing the present invention, a multiplicity of advantages areattainable over the related art. Thus, cracking is reduced during thewelding operation and subsequently thereto. In addition, there is lessdistortion on the structural components due to the narrowerheat-affected zone and the decreased heat input. Higher strengths, aswell as more finely grained weld metal may be obtained during welding,which is consistent with improved quality of the welding process. Areliable repair welding of even extremely thin-walled structuralcomponents is possible. The device according to the present invention isvery versatile. On the one hand, it may be used to weld small structuralcomponents and, on the other hand, large, heavy, and not easilyaccessible structural components, as well. A reproducible weldingquality is derived from the laser pulse control and from the wire feedcontrol. A durable and wear-resistant weld joint is able to be producedby employing the method according to the present invention. Because thecomposition of the structural component to be welded and that of thewelding wire used as filler metal are of like kind, the weld jointformed achieves virtually the same properties as the base material andis thus less susceptible in later operation, in particular to thermalfatigue cracking, since it has the same thermal expansion coefficient asthe base material.

1-19. (canceled)
 20. A method for welding structural components of a gasturbine, comprising operating a laser source in a pulsed mode tolaser-weld a structural component of a gas turbine.
 21. The method asrecited in claim 20, wherein the step of operating the laser sourcefurther comprises: setting one or more of a variably settable pulseduration and a variably settable laser power of the laser source, andwelding the structural component in response to pulses of a laser beamof the laser source.
 22. The method as recited in claim 20, wherein thelaser welding of the structural component is performed withoutpreheating the structural component.
 23. The method as recited in claim20, wherein the laser welding of the structural component is performedin an inert gas atmosphere.
 24. The method as recited in claim 20,further comprising automatically advancing a welding wire into an areaof the laser beam of the laser source.
 25. The method as recited inclaim 24, wherein said step of automatically advancing further comprisescontrolling a wire feed rate of the welding wire as a function of thepulses of the laser beam from the laser source.
 26. The method asrecited in claim 24, wherein said step of automatically advancingfurther comprises controlling a wire feed rate of the welding wire as afunction of one or more of a pulse duration, a pulse shape, and a poweroutput of the laser source.
 27. The method as recited in claim 24,wherein said step of automatically advancing further comprises advancingthe welding wire in response to each pulse of the laser from the lasersource, and wherein a feed rate of the welding wire is a function of thepower output of the laser source.
 28. The method as recited in claim 20,wherein the laser source includes a plurality of laser sources.
 29. Amethod for welding structural components of a gas turbine, comprising:providing a structural component of a gas turbine comprised of adirectionally solidified material or a monocrystalline material; andoperating a laser source in a pulsed mode to laser-weld the structuralcomponent.
 30. A method for welding structural components of a gasturbine, comprising: providing a structural component of a gas turbinecomprised of a nickel-based alloy or of a cobalt-based alloy; andoperating a laser source in a pulsed mode to laser-weld the structuralcomponent.
 31. The method of claim 30, wherein the structural componentcomprises an MCrAlY material.
 32. A device for welding structuralcomponents of a gas turbine, comprising a hand-held laser device, thehand-held device including: at least one laser source; and a controller,the controller controlling an output of the laser source to produce apulsed laser beam.
 33. The device as recited in claim 32, wherein one ormore of a pulse duration a pulse shape and a laser power are variablysettable via the controller.
 34. The device as recited in claim 32,further comprising: a wire feeder coupled to, and controllable by, thecontroller, the wire feeder advancing a welding wire automatically intoa area of the laser beam of the laser source.
 35. The device as recitedin claim 34, wherein the controller is configured to control the wirefeeder such that a wire feed rate of the welding wire is dependent onone or more of a pulse duration, a pulse shape, and a power output ofthe laser source.
 36. The device as recited in claim 32, furthercomprising a holding receptacle for the structural component to bewelded, the laser welding being performable in the holding receptacleunder an inert gas atmosphere.
 37. The device as recited in claims 32,wherein the laser source is a solid-state laser.
 38. The device asrecited in claim 37, wherein the solid-state laser is an Nd-YAG solidstate laser.
 39. The device as recited in claim 37, wherein thesolid-state laser is an optically excited solid-state laser.
 40. Thedevice as recited in claim 39, wherein the optically excited solid-statelaser is one of a diode-pumped solid-state laser and a lamp-pumpedsolid-state laser.
 41. The device as recited in claim 32, wherein thelaser source includes a plurality of laser sources.